Abstract Epigenetic gene reprogramming is an emerging concept relevant to human diseases. This proposal's objective is to investigate epigenetics of severe systemic inflammation (SSI). SSI blood and tissue leukocytes show gene-specific reprogramming with repressed transcription of acute proinflammatory genes like TNF and IL-1 and activated transcription of other gene sets. SSI gene reprogramming reversal correlates with clinical improvement. We reported TNF transcription repression and a nucleosome shift to lysine 9 H3 di-methylation (H3K9me2), H3 serine 10 dephosphorylation(H3S10), and repressor heterochromatin protein 1 (HP-1) promoter binding in an SSI cell model. We further implicate the histone H3 lysine methyltransferase G9a coupled to HP-1 and CpG methylation by cytosine methyltransferase DNMT 3a/b during TNF silencing. Together, these results support that epigenetic mechanisms participate in repressing acute inflammatory genes and sustaining often lethal immunosuppression observed in SSI patients. We hypothesize that SSI generates a shift from a euchromatin (responsive) heterochromatin (silenced) at the proximal promoter of acute proinflammatory genes. Aim 1 will test in whether the euchromatin to heterochromatin shift requires specific H3 serine kinases, lysine methyltransferases and demethylases, and adapters or linkers, and the potential for reversibility. Aim 2 will test whether acute proinflammatory gene promoter CpG methylation is coupled through specific regulatory proteins to the nucleosome shifts. Aim 3 will test whether the epigenetic shift from euchromatin to heterochromatin occurs in circulating human SSI leukocytes. Experimental approaches for the basic (Aims 1 and 2) and translational aims (Aim 3) will include genetic (transfection of siRNA or expression plasmids) and biochemical (chromatin immunoprecipitation, DNA sequencing, DNAase footprinting, immunoblots, and mRNA quantitation) analyses. *